The present invention relates to a data transmission method for transmitting (including recording and reproducing) digital signals representing audio information or the like.
Conventionally, a reproducing apparatus as shown in FIG. 1 has been used at a reception side of a data transmission system of this type. In FIG. 1, a data input carrying, for example, audio information transmitted and demodulated by a suitable demodulator is compared with a reference voltage by a comparator 1, shaped into a digital signal having steep leading and trailing edges, and then supplied to a memory control circuit 2. Employing synchronization derived from a clock component extracted from the supplied digital signal, the memory control circuit 2 successively writes the information data and check word (parity bit) in the digital signal into a buffer memory 3. Upon completion of the writing operation, the data is successively read out of the buffer memory 3 and supplied to an error detection correction circuit 4 where, if there is an error bit in the information data, the location of the error bit is detected and the error corrected. The thus-corrected data is successively read out and converted into the original audio signal by a D/A converter 5. In the data reproducing apparatus as described above, the coding method in which the check word added at the transmitter side is based is fixed, and error detection correction operations are performed corresponding to the coding method.
In such a data transmission system, in the case where a single type of information is to be transmitted, it is sufficient to employ a coding method having necessary redundancy and capability of error correction in accordance with the type of the information, and therefore there are no particular problems. However, where a plurality of types of information, for example, such as audio information having a relatively high self correlation and computer program information having a low self correlation, are to be transmitted, the coding method should be different for the two different types of data. For instance, in the case of transmitting by way of the same tranceiver both computer programs and audio signals digitized by an ADM (Adaptive Delta Modulation) system, the coding method is chosen such that the probability of data error correction for the computer programs is acceptably high, the coding method becomes nonoptimum when applied to the audio signals because the data correction is performed with an unnecessarily high quality.